Compare two array of objects and add the objects with matching values to the first array of objects

Question

I have 2 array of objects that look like this

var pollAnswers = [
        {
            "_id": "5b58afa0c767e12c9869e540",
            "pollId": "5b58afa0c767e12c9869e53f",
            "option": "Google",
        },
        {
            "_id": "5b58afa0c767e12c9869e541",
            "pollId": "5b58afa0c767e12c9869e53f",
            "option": "The Jetsons",
        },
        {
            "_id": "5b58afa0c767e12c9869e542",
            "pollId": "5b58afa0c767e12c9869e53f",
            "option": "Family  Guy",
        },
        {
            "_id": "5b593b195c420e28089daf9d",
            "pollId": "5b593b195c420e28089daf9c",
            "option": "Yes. Through loyalty programmes.",
        },
        {
            "_id": "5b593b195c420e28089daf9e",
            "pollId": "5b593b195c420e28089daf9c",
            "option": "What Hunger Crisis?",
        },
        {
            "_id": "5b5953d775c4401e7052127c",
            "pollId": "5b5953d775c4401e7052127b",
            "option": "Yes, absolutely",
        },
        {
            "_id": "5b5953d775c4401e7052127d",
            "pollId": "5b5953d775c4401e7052127b",
            "option": "No, absolutely not",
        }
    ]

var polls = [
        {
            "_id": "5b58afa0c767e12c9869e53f",
            "pollName": "Consumers in 2070 (How about now?)",
            "pollQuestion": "Which animated series will consumers in 2070 resemble the most?",
        },
        {
            "_id": "5b593b195c420e28089daf9c",
            "pollName": "World Hunger",
            "pollQuestion": "Can Internet-based services solve the Hunger Crisis?",
        },
        {
            "_id": "5b5953d775c4401e7052127b",
            "pollName": "Make things Work Again",
            "pollQuestion": "Make things Work",
        }
    ]

I need to compare the pollId from pollAnsers with _id in polls to add the matching answers to the corresponding pollQuestions in the following way

"polls": [
        {
            "_id": "5b58afa0c767e12c9869e53f",
            "pollName": "Consumers in 2070 (How about now?)",
            "pollQuestion": "Which animated series will consumers in 2070 resemble the most?",
            "answersList": [
              {
                "_id": "5b58afa0c767e12c9869e540",
                "pollId": "5b58afa0c767e12c9869e53f",
                "option": "Google",
              },
              {
                "_id": "5b58afa0c767e12c9869e541",
                "pollId": "5b58afa0c767e12c9869e53f",
                "option": "The Jetsons",
              },
              {
                "_id": "5b58afa0c767e12c9869e542",
                "pollId": "5b58afa0c767e12c9869e53f",
                "option": "Family  Guy",
              },             
            ]
        },
        {
            "_id": "5b593b195c420e28089daf9c",
            "pollName": "World Hunger",
            "pollQuestion": "Can Internet-based services solve the Hunger Crisis?",
            "answersList": [
                {
                  "_id": "5b593b195c420e28089daf9d",
                  "pollId": "5b593b195c420e28089daf9c",
                  "option": "Yes. Through loyalty programmes.",
                },
                {
                  "_id": "5b593b195c420e28089daf9e",
                  "pollId": "5b593b195c420e28089daf9c",
                  "option": "What Hunger Crisis?",
                }
            ]
        },
        {
            "_id": "5b5953d775c4401e7052127b",
            "pollName": "Make things Work Again",
            "pollQuestion": "Make things Work",
            "answersList": [
              {
                "_id": "5b5953d775c4401e7052127c",
                "pollId": "5b5953d775c4401e7052127b",
                "option": "Yes, absolutely",
              },
              {
                "_id": "5b5953d775c4401e7052127d",
                "pollId": "5b5953d775c4401e7052127b",
                "option": "No, absolutely not",
              }
            ]
        }
    ]

I have been trying all possibilities like using map, filter, for loops etc but haven't been able to get the result, I am fairly new to this please help ! thanks

@mplungjan I did search for literally 2 hours but since I am newbie to javascript I was not able to get the right way to apply things. — hushie
– hushie, Commented Jul 27, 2018 at 9:24

Ankit Agarwal · Accepted Answer · 2018-07-27 08:48:58Z

You can use two forEach() loops with simple and understandable code:

var pollAnswers = [
        {
            "_id": "5b58afa0c767e12c9869e540",
            "pollId": "5b58afa0c767e12c9869e53f",
            "option": "Google",
        },
        {
            "_id": "5b58afa0c767e12c9869e541",
            "pollId": "5b58afa0c767e12c9869e53f",
            "option": "The Jetsons",
        },
        {
            "_id": "5b58afa0c767e12c9869e542",
            "pollId": "5b58afa0c767e12c9869e53f",
            "option": "Family  Guy",
        },
        {
            "_id": "5b593b195c420e28089daf9d",
            "pollId": "5b593b195c420e28089daf9c",
            "option": "Yes. Through loyalty programmes.",
        },
        {
            "_id": "5b593b195c420e28089daf9e",
            "pollId": "5b593b195c420e28089daf9c",
            "option": "What Hunger Crisis?",
        },
        {
            "_id": "5b5953d775c4401e7052127c",
            "pollId": "5b5953d775c4401e7052127b",
            "option": "Yes, absolutely",
        },
        {
            "_id": "5b5953d775c4401e7052127d",
            "pollId": "5b5953d775c4401e7052127b",
            "option": "No, absolutely not",
        }
    ]

var polls = [
        {
            "_id": "5b58afa0c767e12c9869e53f",
            "pollName": "Consumers in 2070 (How about now?)",
            "pollQuestion": "Which animated series will consumers in 2070 resemble the most?",
        },
        {
            "_id": "5b593b195c420e28089daf9c",
            "pollName": "World Hunger",
            "pollQuestion": "Can Internet-based services solve the Hunger Crisis?",
        },
        {
            "_id": "5b5953d775c4401e7052127b",
            "pollName": "Make things Work Again",
            "pollQuestion": "Make things Work",
        }
];

polls.forEach((poll) => {
  poll.answerList = [];
  pollAnswers.forEach((pollAnswer) => {
    if(pollAnswer.pollId === poll._id){
      poll.answerList.push(pollAnswer);
    }
  });
});
console.log(polls);

31piy · Accepted Answer · 2018-07-27 08:51:57Z

You can loop over the polls using Array#forEach, in each iteration, find the related answers using Array#filter, and assign them to the poll object:

var pollAnswers = [{"_id":"5b58afa0c767e12c9869e540","pollId":"5b58afa0c767e12c9869e53f","option":"Google"},{"_id":"5b58afa0c767e12c9869e541","pollId":"5b58afa0c767e12c9869e53f","option":"The Jetsons"},{"_id":"5b58afa0c767e12c9869e542","pollId":"5b58afa0c767e12c9869e53f","option":"Family  Guy"},{"_id":"5b593b195c420e28089daf9d","pollId":"5b593b195c420e28089daf9c","option":"Yes. Through loyalty programmes."},{"_id":"5b593b195c420e28089daf9e","pollId":"5b593b195c420e28089daf9c","option":"What Hunger Crisis?"},{"_id":"5b5953d775c4401e7052127c","pollId":"5b5953d775c4401e7052127b","option":"Yes, absolutely"},{"_id":"5b5953d775c4401e7052127d","pollId":"5b5953d775c4401e7052127b","option":"No, absolutely not"}];
var polls = [{"_id":"5b58afa0c767e12c9869e53f","pollName":"Consumers in 2070 (How about now?)","pollQuestion":"Which animated series will consumers in 2070 resemble the most?"},{"_id":"5b593b195c420e28089daf9c","pollName":"World Hunger","pollQuestion":"Can Internet-based services solve the Hunger Crisis?"},{"_id":"5b5953d775c4401e7052127b","pollName":"Make things Work Again","pollQuestion":"Make things Work"}];

polls.forEach(poll => {
  poll.answersList = pollAnswers.filter(ans => ans.pollId === poll._id);
})

console.log(polls);

Nina Scholz · Accepted Answer · 2018-07-27 08:55:57Z

You could take the power of Map and iterate the target array first to fill the map and generate independent objects for the result set.

Then iterate all answers and assign them to the associated polls.

var pollAnswers = [{ _id: "5b58afa0c767e12c9869e540", pollId: "5b58afa0c767e12c9869e53f", option: "Google" }, { _id: "5b58afa0c767e12c9869e541", pollId: "5b58afa0c767e12c9869e53f", option: "The Jetsons" }, { _id: "5b58afa0c767e12c9869e542", pollId: "5b58afa0c767e12c9869e53f", option: "Family  Guy" }, { _id: "5b593b195c420e28089daf9d", pollId: "5b593b195c420e28089daf9c", option: "Yes. Through loyalty programmes." }, { _id: "5b593b195c420e28089daf9e", pollId: "5b593b195c420e28089daf9c", option: "What Hunger Crisis?" }, { _id: "5b5953d775c4401e7052127c", pollId: "5b5953d775c4401e7052127b", option: "Yes, absolutely" }, { _id: "5b5953d775c4401e7052127d", pollId: "5b5953d775c4401e7052127b", option: "No, absolutely not" }],
    polls = [{ _id: "5b58afa0c767e12c9869e53f", pollName: "Consumers in 2070 (How about now?)", pollQuestion: "Which animated series will consumers in 2070 resemble the most?" }, { _id: "5b593b195c420e28089daf9c", pollName: "World Hunger", pollQuestion: "Can Internet-based services solve the Hunger Crisis?" }, { _id: "5b5953d775c4401e7052127b", pollName: "Make things Work Again", pollQuestion: "Make things Work" }],
    map = new Map,
    result = {
        polls: polls.map(p => {
            var answersList = [];
            map.set(p._id, answersList);
            return Object.assign({}, p, { answersList });
        })
    };

pollAnswers.forEach(p => map.get(p.pollId).push(p));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

I now get what mistake I was making when I tried to use map ! thanks

mpm · Accepted Answer · 2018-07-27 08:56:54Z

My solution with reduce :

   var pollsWithAnswers = pollAnswers.reduce(function(polls, answer) {
      var index = polls.findIndex(function(pol) {
        return pol._id == answer.pollId;
      })
      if (index > -1) {
        if (polls[index].anwerList instanceof Array) polls[index].anwerList.push(answer);
        else polls[index].anwerList = [answer]
      }
      return polls
    }, polls.slice())

var pollAnswers = [{
    "_id": "5b58afa0c767e12c9869e540",
    "pollId": "5b58afa0c767e12c9869e53f",
    "option": "Google",
  },
  {
    "_id": "5b58afa0c767e12c9869e541",
    "pollId": "5b58afa0c767e12c9869e53f",
    "option": "The Jetsons",
  },
  {
    "_id": "5b58afa0c767e12c9869e542",
    "pollId": "5b58afa0c767e12c9869e53f",
    "option": "Family  Guy",
  },
  {
    "_id": "5b593b195c420e28089daf9d",
    "pollId": "5b593b195c420e28089daf9c",
    "option": "Yes. Through loyalty programmes.",
  },
  {
    "_id": "5b593b195c420e28089daf9e",
    "pollId": "5b593b195c420e28089daf9c",
    "option": "What Hunger Crisis?",
  },
  {
    "_id": "5b5953d775c4401e7052127c",
    "pollId": "5b5953d775c4401e7052127b",
    "option": "Yes, absolutely",
  },
  {
    "_id": "5b5953d775c4401e7052127d",
    "pollId": "5b5953d775c4401e7052127b",
    "option": "No, absolutely not",
  }
]

var polls = [{
    "_id": "5b58afa0c767e12c9869e53f",
    "pollName": "Consumers in 2070 (How about now?)",
    "pollQuestion": "Which animated series will consumers in 2070 resemble the most?",
  },
  {
    "_id": "5b593b195c420e28089daf9c",
    "pollName": "World Hunger",
    "pollQuestion": "Can Internet-based services solve the Hunger Crisis?",
  },
  {
    "_id": "5b5953d775c4401e7052127b",
    "pollName": "Make things Work Again",
    "pollQuestion": "Make things Work",
  }
]


console.log(pollAnswers.reduce(function(polls, answer) {
  var index = polls.findIndex(function(pol) {
    return pol._id == answer.pollId;
  })
  if (index > -1) {
    if (polls[index].anwerList instanceof Array) polls[index].anwerList.push(answer);
    else polls[index].anwerList = [answer]
  }
  return polls
}, polls.slice()))

Thanks this works too ! I tried reduce but did not know where I was going wrong

deerawan · Accepted Answer · 2018-07-27 11:00:46Z

This is another solution to use map and filter with simple and immutable way so your original arrays will not be mutated.

var pollAnswers = [{"_id":"5b58afa0c767e12c9869e540","pollId":"5b58afa0c767e12c9869e53f","option":"Google"},{"_id":"5b58afa0c767e12c9869e541","pollId":"5b58afa0c767e12c9869e53f","option":"The Jetsons"},{"_id":"5b58afa0c767e12c9869e542","pollId":"5b58afa0c767e12c9869e53f","option":"Family  Guy"},{"_id":"5b593b195c420e28089daf9d","pollId":"5b593b195c420e28089daf9c","option":"Yes. Through loyalty programmes."},{"_id":"5b593b195c420e28089daf9e","pollId":"5b593b195c420e28089daf9c","option":"What Hunger Crisis?"},{"_id":"5b5953d775c4401e7052127c","pollId":"5b5953d775c4401e7052127b","option":"Yes, absolutely"},{"_id":"5b5953d775c4401e7052127d","pollId":"5b5953d775c4401e7052127b","option":"No, absolutely not"}];
var polls = [{"_id":"5b58afa0c767e12c9869e53f","pollName":"Consumers in 2070 (How about now?)","pollQuestion":"Which animated series will consumers in 2070 resemble the most?"},{"_id":"5b593b195c420e28089daf9c","pollName":"World Hunger","pollQuestion":"Can Internet-based services solve the Hunger Crisis?"},{"_id":"5b5953d775c4401e7052127b","pollName":"Make things Work Again","pollQuestion":"Make things Work"}];

const pollsWithAnswers = polls.map(poll => ({
   ...poll,
   answersList: pollAnswers.filter(answer => poll._id === answer.pollId) 
}));

console.log(pollsWithAnswers);

Hope it helps

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